Abstract

Morphological examination of the Aromatum Chaos depression on Mars supports earlier suggestions that it is a site of cryosphere disruption and release of pressurized water trapped in an underlying aquifer. We infer that the cause of cryosphere disruption was intrusion of a volcanic sill, confined laterally by earlier intruded dikes, and consequent melting of ice by heat from the sill. The vertical extents and displacements of blocks of terrain on the floor of the depression, together with an estimate of the cryosphere thickness, constrain the vertical extent of ice melting and hence the thickness of the sill (∼100 m) and the depth at which it was intruded (∼2–5 km). At least ∼75% of the volume of material removed from Aromatum Chaos must have been crustal rock rather than melted ice. Water from melted cryosphere ice played a negligible role in creating the depression, the process being dominated by released aquifer water. For sediment loads of 30–40% by volume, 10,500–16,500 km3 of aquifer water must have passed through the depression to carry away rock as entrained sediment and erode the associated Ravi Vallis channel. These required water volumes are 2–3 times larger than the amount of water that could reasonably be contained in aquifers located beneath the area of incipiently collapsed ground to the west of Aromatum Chaos and suggest a much larger water source. Given that this source probably also fed the nearby Shalbatana Vallis outflow channel, Gangis Chasma is the most likely candidate.